[Bug rtl-optimization/126276] [17 Regression] Recent change breaks cris-elf

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126276

--- Comment #8 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
I think I got it: ideally, the fix should have been local to the "*btst<mode>"
pattern: no need to change the mode of the *result* of the zero_extract, as
it's inherently zero-extending (see rtl.texi).

That also means that the r17-2413 could drop the "precision <=
GET_MODE_UNIT_PRECISION (GET_MODE (XEXP (op, 0)))" condition for
zero_extract...I think.

Also spotted missing define_insn_and_split:s in cris.md for btst from cstore,
not just cbranch.

Let's see if I can get any or all of those done.